Screw-propeller.



H. E. McDONALD. SCREW PROPELLE R.

APPLICATION FILED APR-18,1914.

Patented Aug. 10, 1915.

2 SHEETS-SHEET 1.

Patented Aug. 10, 1915.

2 SHEETS-SHEET 2- cm, WASHINGTON n c HENRY EDWIN MCDONALD, or sYDNEY, .NEW scorn WALES, AUsritALIA.

SCREW-PROPELLER.

Application filed April 18, 1914.

The invention comprises the usual rota-v table shaft having a two or more bladed helical screw secured to a boss thereon or cast integral therewith said boss being preferably longer than is usual.

on each side of the boss. Each blade has arms secured thereto on which is held an outer blade curving inwar ly at an angle. The edge of each outer blade is formed with aflange for the whole or portion of its length. angle of about 30 to 60 to the axial line of the shaft while the inner blades are secured to the boss at an angle of about 4-5 Between the inner and outer blades is a clearance or space for the water to pass the effect of which is to avoid cavitation and tends to minimize pitching and slip. But in order that the invention may be readily comprehended, I refer now to the drawings herewith, in which 2- Figure l is anelevation, and, Fig. 2 a vertical elevation of leading end; Figs. 3 and 4 being sectional elevations on the arrows 38 and a l respectively on the line A E. Fig. 5 is a section through the two blades.

Like numerals indicate like parts. I

6 is the shaft on which is the boss 7 carrying the inner helical blades 8 and 9 curved at an angle of about 45. At the leading end of the said blades arms 10 and 11 secure the ends of the flanged outer helical blades 12 and 13 which in the drawings are shown at an angle of about 60, their trail- Specification of Letters Batent.

Each blade is double that is to say it extends diagonally The outer blades are secured at an' Patented Aug. 19, 1915.

Serial No. 832,950.

iiig ends being secured by the arms or straps 14 and 15 to the inner blades 9 and 8 respectively. Additional strengthening arms as 16 are preferably provided and may be so twisted as to ofier a minimum of resistance. I have shown the outer blade 12 secured at the trailing end by the strap 14 to the inner blade 9 and the blade l3bythe strap 15 to the inner blade Sbut they may be secured by short arms as at the leading end to the same inner blades as they are connected to or they may be attached to the boss.

The inclination of the inner blades to the aXis is substantially constant but the inclination of the outer blades may vary according to the character of the body to be propelled.

My theory is that on rotation of the shaft as much effective work will be performed at the'boss as at the external ends of the illnei' blades and with a free body of water between the inner and outer blades cavitation is avoided while the flanges on the outer blades prevent slip.

Having now described my invention, what I claim as new and desire to protect by Letters Patent, is

1. In screw propellers the combination with a rotatable shaft of two or more inner helical blades on a boss thereon and two or more outer helical blades of a different inclination to the axis and secured to said inner blades by arms substantially as dc scribed. V

2. In screw propellers the combination with a rotatable shaft of two or more inner helical blades on a boss thereon inclined at an angle of about 15 and. two or more outer helical blades inclined at an angle of from to and secured to said inner blades by arms or straps said outer blades being flanged substantially as described.

In testimony whereof I have hereunto set my hand in presence of two subscribing witnesses.

HENRY EDWIN llloDONALD.

Witnesses CHARLEs E. GRAHAM, HENRY lV. CLARKE.

Copies of this patent maybe obtained for five cents each, by addressing the Commissioner of Patents,

. Washington, 11.0. 

